/*
   This is the 3rd version of SwingWorker (also known as SwingWorker 3), an
   abstract class that you subclass to perform GUI-related work in a dedicated
   thread. For instructions on and examples of using this class, see:

   http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html

   Note that the API changed slightly in the 3rd version: You must now invoke
   start() on the SwingWorker after creating it.

   Copyright (C) 2006-2008 Carnegie Mellon University

   Tim Vidas <tvidas at gmail d0t com>
   Brian Kaplan <bfkaplan at cmu d0t edu>


   This program is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by the Free
   Software Foundation; either version 2 of the License, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful, but WITHOUT
   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
   more details.

   You should have received a copy of the GNU General Public License along with
   this program; if not, write to the Free Software Foundation, Inc., 59 Temple
   Place, Suite 330, Boston, MA 02111-1307 USA
*/

package cmu.forensics.openlv;
import javax.swing.SwingUtilities;

public abstract class SwingWorker
{
    private Object	value;	// see getValue(), setValue()

    /**
     * Class to maintain reference to current worker thread under separate
     * synchronization control.
     */
    private static class ThreadVar
    {
        private Thread	thread;

        ThreadVar(Thread t)
        {
            thread = t;
        }

        synchronized Thread get()
        {
            return thread;
        }

        synchronized void clear()
        {
            thread = null;
        }
    }

    private ThreadVar	threadVar;

    /**
     * Get the value produced by the worker thread, or null if it hasn't been
     * constructed yet.
     */
    protected synchronized Object getValue()
    {
        return value;
    }

    /**
     * Set the value produced by worker thread
     */
    private synchronized void setValue(Object x)
    {
        value = x;
    }

    /**
     * Compute the value to be returned by the <code>get</code> method.
     */
    public abstract Object construct();

    /**
     * Called on the event dispatching thread (not on the worker thread) after
     * the <code>construct</code> method has returned.
     */
    public void finished()
    {}

    /**
     * A new method that interrupts the worker thread. Call this method to force
     * the worker to stop what it's doing.
     */
    public void interrupt()
    {
        Thread t = threadVar.get();
        if (t != null)
        {
            t.interrupt();
        }
        threadVar.clear();
    }

    /**
     * Return the value created by the <code>construct</code> method. Returns
     * null if either the constructing thread or the current thread was
     * interrupted before a value was produced.
     * 
     * @return the value created by the <code>construct</code> method
     */
    public Object get()
    {
        while (true)
        {
            Thread t = threadVar.get();
            if (t == null)
            {
                return getValue();
            }
            try
            {
                t.join();
            }
            catch (InterruptedException e)
            {
                Thread.currentThread().interrupt(); // propagate
                return null;
            }
        }
    }

    /**
     * Start a thread that will call the <code>construct</code> method and
     * then exit.
     */
    public SwingWorker()
    {
        final Runnable doFinished = new Runnable()
        {
            public void run()
            {
                finished();
            }
        };

        Runnable doConstruct = new Runnable()
        {
            public void run()
            {
                try
                {
                    setValue(construct());
                }
                finally
                {
                    threadVar.clear();
                }

                SwingUtilities.invokeLater(doFinished);
            }
        };

        Thread t = new Thread(doConstruct);
        threadVar = new ThreadVar(t);
    }

    /**
     * Start the worker thread.
     */
    public void start()
    {
        Thread t = threadVar.get();
        if (t != null)
        {
            t.start();
        }
    }
}
